Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to an array substrate for a liquid crystal display (LCD) device having a repair pattern and a method of fabricating the array substrate.
Background for the Related Art
In general, a liquid crystal display (LCD) device utilizes optical anisotropy and polarization properties of liquid crystal molecules. The liquid crystal molecules have a definite alignment direction as a result of their thin and long shapes. The alignment direction of the liquid crystal molecules can be controlled by applying an electric field across the liquid crystal molecules. In other words, as the intensity or direction of the electric field is changed, the alignment of the liquid crystal molecules also changes. Since incident light is refracted based on the orientation of the liquid crystal molecules due to the optical anisotropy of the liquid crystal molecules, images can be displayed by controlling light transmissivity.
The LCD device includes an upper substrate where a common electrode is formed, a lower substrate where a pixel electrode is formed, and a liquid crystal layer interposed between the upper substrate and the lower substrate. The upper and lower substrates may be referred to as a color filter substrate and an array substrate, respectively. The liquid crystal layer is driven by a vertical electric field induced between the common and pixel electrodes such that a light transmittance and an aperture ratio of the LCD device are excellent. An active matrix LCD (AM-LCD) device includes a thin film transistor (TFT) as a switching element, and since it has excellent characteristics of high resolution and displaying moving images, the AM-LCD device has been widely utilized.
FIG. 1 is an exploded perspective view that schematically illustrates such an AM-LCD device according to the related art. As shown in FIG. 1, the LCD device includes an array substrate 10, a color filter substrate 20, and a liquid crystal layer 30. The array substrate 10 and the color substrate 20 face each other, and the liquid crystal layer 30 is interposed therebetween. The array substrate 10 includes a first substrate 12 on which a gate line 14, a data line 16, a TFT “Tr” and a pixel electrode 18 are formed. The gate line 14 and the data line 16 cross each other, thereby forming a region between the gate and data lines 14 and 16. The region is defined as a pixel region “P”. The TFT “Tr” is formed at a crossing portion between the gate and data lines 14 and 16, and the pixel electrode 18 is formed in the pixel region “P” and connected to the TFT “Tr”.
The color filter substrate 20 includes a second substrate 22 on which a black matrix 25, a color filter layer 26 and a common electrode 28 are formed. The black matrix 25 has a lattice shape to cover a non-display region of the first substrate 12, such as the gate line 14, the data line 16, the TFT “Tr”. The color filter layer 26 includes first, second and third sub-color filters 26a, 26b and 26c. Each of the sub-color filters 26a, 26b and 26c has one of red, green and blue colors R, G and B and corresponds to the each pixel region “P”. The common electrode 28 is formed on the black matrix 25 and the color filter layers 26 and over an entire surface of the second substrate 22.
Although not shown, to prevent the liquid crystal layer 30 from leaking, a seal pattern may be formed along edges of the first and second substrates 12 and 22. First and second alignment layers may be formed between the first substrate 12 and the liquid crystal layer 30 and between the second substrate 22 and the liquid crystal layer 30. A polarizer may be formed on an outer surface of the first and second substrates 12 and 22. The LCD device also includes a backlight assembly opposing an outer surface of the first substrate 12 to supply light to the liquid crystal layer 30. When a scanning signal is applied to the gate line 14 to control the TFT “Tr”, a data signal is applied to the pixel electrode 18 through the data line 16 such that the electric field is induced between the pixel and common electrodes 18 and 28. Then, the electric field causes the liquid crystals to switch on and as a result, the LCD device produces images using the light from the backlight assembly.
FIG. 2 is a plan view schematically illustrating a portion of an array substrate for the related art LCD device. In FIG. 2, a plurality of gate lines 14 are formed on the array substrate 10. The gate lines 14 are spaced apart from each other. Although not shown, a gate pad for connecting to an external driving circuit substrate is formed at one end of the gate line 14. A data line 16, which crosses the gate line 14 to define a pixel region P, is formed on the array substrate 10. A data pad (not shown) for connecting to an external driving circuit substrate (not shown) is formed at one end of the data line 16. A thin film transistor (TFT) Tr including a gate electrode 15, a semiconductor layer 40, a source electrode 43 and a drain electrode 47 is formed at a crossing portion (overlapped portion) of the gate and data lines 14 and 16. A pixel electrode 18 is formed in each pixel region P. The pixel electrode 18 is connected to the TFT Tr. The pixel electrode 18 overlaps the gate line 14, thereby forming a storage capacitor StgC to maintain a present voltage until a next signal is applied into the pixel electrode 18.
The array substrate 10 may be formed through four or five mask processes. For example, each mask process may further include five steps: a step of forming a photoresist (PR) layer on a material layer, a step of exposing the PR layer using a mask, a step of developing the PR layer to form a PR pattern, a step of etching the material layer using the PR pattern as an etching mask, and a step of stripping the PR pattern. Thus, twenty or twenty-five steps are needed to form the array substrate 10. During these steps, an electrical short or electrical opening problem by static electricity or metallic particles may occur, when the metallic particles are attached to the gate line 14, the data line 16, or the TFT Tr. In such a situation, a voltage is continuously applied into the pixel electrode 18 or no voltage is applied into the pixel electrode 18. As a result, ON or OFF state of the pixel electrode 18 cannot be controlled such that all pixel regions P along the corresponding gate line 14 or the data line 16 always have an ON or OFF state.
The LCD devices have several ten thousands to several millions pixel regions depending on their sizes and resolutions. Therefore, failure costs can be high when there are requirements in all of these pixel regions to have a desired condition. Accordingly, some defective pixels in the LCD device are endured (absorptive). However, when an electrical short occurs in a crossing portion of the gate and data lines 14 and 16, there is a bright or dark spot problem in all pixel regions connected to corresponding gate and data lines 14 and 16, thereby causing the LCD device to be rendered unacceptable. This problem is also referred to as a line defect. However, when there is a defect in merely one or several pixels, the LCD device can be available, and this defect is referred to as a dot defect.
Recently, in order to improve a high quality displaying image, a repair process has been proposed to repair the LCD device having the dot defect. Specifically, in a normally white mode LCD device, a white image is displayed when no voltage is applied and a black image is displayed when a maximum voltage is applied. Since a defective pixel always displays a white image and thus stands out conspicuously, the repair process is required to change the defective pixel into a pixel that always displays a black image. That is, a white-colored defective pixel is repaired to change into a black-colored defective pixel. The reason for this repair process is that a white pixel in a black base is much more prominent than the other scenario. Accordingly, by repairing a white-colored defective pixel into a black-colored defective pixel without repairing a black-colored defective pixel, and acceptable LCD is provided.
FIG. 3 is a plan view schematically illustrating the repairing process for the array substrate of the LCD device according to the related art. As shown in FIG. 3, in a normally white mode LCD device, when there is a white-colored defect in a pixel region P of an array substrate, a TFT Tr is disconnected from a pixel electrode 18 by irradiating a laser onto a cutting line CL, and a portion of the pixel electrode 18, which overlaps a portion of the gate line 14, is electrically connected to the portion of the gate line 14 by irradiating a laser onto a connecting portion CP such that a voltage is continuously applied into the pixel electrode 18 in the pixel region P. As a result, the pixel region P has a black-colored defective state.
On the other hand, in a normally black mode LCD device, when there is a white-colored defect in a pixel region for an array substrate, a TFT is disconnected from a pixel electrode by irradiating a laser onto a cutting line CL without connecting the pixel electrode to the gate line such that no voltage is applied into the pixel electrode in the pixel region. As a result, the pixel region P has a black-colored defective state. However, the above repairing process is available only for a dot defect and not for a line defect. Accordingly, the LCD device having the line defect cannot be repaired, thereby decreasing a production yield, and increasing failure costs and production costs.